Laminated cores for transformers and reactors



Jan. 2, 1962 O 3,015,791

LAMINATED CORES FOR TRANSFORMERS AND REACTORS Filed April 11, 1952 3,015,791 LAMENATED CORES FOR TRANSFORMERS AND REACTQRS Erich Rolf, Nurnberg, Germany, assignor to Siemens- Schuckettwerke Aktiengesellschaft, Eerlin-Siemensstadt,

Germany, a corporation of Germany Filed Apr. 11, 1952, Ser. No. 281,831 Claims priority, application Germany Apr. 18, 1951 Claims. (Cl. 336-217) My invention relates to laminated magnetizable core structures for transformers, reactors and other electrically inductive devices.

In the design of magnetizable high-quality cores for transformers and reactors increasing attention is being given to the use of ferromagnetic materials of a preferred magnetic orientation. For any given field strength and hence any given magnetizing current, such cores admit a larger magnetic induction than is otherwise obtainable and thus permit corresponding savin s in Weight. The superior magnetic properties of sheet material having a preferred magnetic orientation can best be realized in wound strip cores of annular shape. Therefore such cores are now being given preference for certain exacting applications, such as in the commutating reactors of contact converters. However, the mounting of the windings on wound cores is more time-consuming and expensive, and the utilization of the available winding space obtainable thereby is more limited than with rectangular cores. It is therefore often desirable to stack the cores from punched or cut sheets rather than winding them from strip material.

On the other hand, in the conventional design of stacked lamination cores, the necessary junction gaps greatly impair the magnetization characteristic and thus tend to diminish the advantages of a preferred magnetic orientation. Also to be considered is the fact that with silicon iron, in contrast to nickel iron, punched sheets cannot be used to advantage if the magnetic flux lines extend, though only partially, transversely to the rolling direction. This is so because silicon iron has only one preferred magnetic orientation, and this orientation is coincident with the rolling direction. In this respect, the material differs from nickel iron which has two preferred orientations in the plane of the sheet, one being coincident with the rolling direction and the other per penclicular thereto. In the transverse direction the magnetic properties of silicon iron laminations are so markedly inferior that cores of silicon iron must be so disigned that the rolling direction of the sheet material is everywhere identical with the direction of the magnetic lines of flux.

In a known lamina-ted core of rectangular frame shape, the individual'laminations consist of rectangular strips and the junction gaps at two parallel frame sides lie perpendicular to the strip direction and are alternately displaced relative to each other. This permits placing all strips with their rolling direction in line with the flux direction. However, at each junction gap nearly the entire flux from the lamination layer interrupted by that gap passes temporarily through the adjacent layers, which are continuous beside the gap. Consequently, the magnetic induction in the adjacent layers is about twice as high locally beside the gap as in the other portions. Hence, at these localities the iron is already saturated when the induction in the other portions is only about half as large as the saturation induction B In other words, when in the major portions of the core the induction value B /Z is exceeded, the saturated iron next to the gaps starts acting like an air gap. Hence, above the value B /Z a more or less pronounced break or shearing occurs in the magnetization characteristic depending upon the length of the junction gaps. For that reason the iron can be utilized with only about one half of the saturation induction if the magnetizing current is to remain at the same small magnitude.

It is known, for improving the magnetic conditions, to place the butt gaps not into the geometrical extensions of the frame-opening sides but in a diagonal direction at an angle of about 45. The alternate gap displacement is effected by displacing each alternate strip of the longitudinal frame portions (limbs) parallel to itself in its longitudinal direction and to reverse the pertaining transverse frame portions (yokes). The required strip shapes result in an enlarged cross section of the yoke portion. This design reduces the induction beside the gaps but does not sufficiently eliminate the impairment of the magnetic characteristic which remains sheared at inductions above about 0.718 The gap displacement in such cores does not affect their angular relation. That is, all junction gaps at any one corner of the frame structure have the same direction, the gaps in adjacent layers being parallel to one another.

It is an object of my invention to devise a magnetizable core structure which, though composed of individual laminations, affords a greatly improved magnetization characteristic by reducing the detrimental effect of the butt gaps down to its virtual elimination.

To this end, according to my invention, the sheet laminations of a frame-shaped core structure are so shaped and assembled that at each corner of the frame structure the gap edges to be traversed by the flux have respectively different angular directions in the manner explained in the following with reference to the drawing in which:

FIG. 1 shows a front View of a portion of a rectangular core structure according to the invention, and FIG. 2 shows schematically a cross section of the structure along the plane indicated in FIG. 1 at IIlI;

FIG. 3 shows a front view of somewhat modified lamination strips applicable in cores otherwise corresponding to FIGS. 1 and 2;

FIG. 4 shows a front view and FIG. 5 a schematic cross section of another core structure according to the invention, the section plane of FIG. 5 being indicated in FIG. 4 at V-V; and

FIG. 6 shows a partial front view of a multi-legged core structure also embodying the invention.

The same reference numerals are applied in all illustrations to similar respective elements.

In the core shown in FIGS. 1 to 6, each individual corner portion of the frame-shaped structure is composed of differently designed lamination layers. In the layers of one of said designs, a limb strip with a diagonal edge abuts at the corner against a diagonal edge of a yoke strip. In the layers of the other design, in the same corner, a limb strip extends rectangularly up to the full height of the yoke strip; that'layer of the corner is therefore formed only by the limb strip. 7

In the core shown in FIGS. 1 and 2, the butt gaps of part of the punched lamination strips extend diagonally. The strips of the yoke 7 have twice the Width of the strips of the limb 8. Each alternate layer of the core is a complete frame, the opposite sides of which are comprised of diagonally abutting strips '7 and ii. The-intermediate layers have only limb strips 8" of rectangular shape that extend over the whole width of the yoke portion. Consequently, the limb portions 8', 8 of the core are completely filled with iron, while the middle parts of the yoke portions are filled only 50%. The induction in the middle parts of the yokes therefore has the same magnitude as the induction in the limb portions. However, at the junction gaps where the total flux from two strips passes through only one, here continuous strip,

the magnitude of induction is 2/ B or approximately 0.913, assuming that the density of the flux lines is uniform along the entire length of the gap. Actually the induction is somewhat higher because the lines of force do not penetrate to the outermost point of the corner. However, the induction does not appreciably exceed the value B. Hence, theinvention satisfies the aim to keep the induction beside the junction gaps at a value not higher than that obtaining in the other core parts while requiring an only slight increase in weight as compared with the known core design.

For a laminated core according to FIGS. 1 and 2, without yoke enlargement, three difi'erent shapes of punchings are needed, namely one for the yoke strips, another one for the bevelled limb strips, and the third for the rectangular limb strips.

It is also possible to compose the core of punchings of only two ditterent shapes. An individual layer of such a core is illustrated in FIG. 3. ,The layer is U-shaped and consists of a trapezoidal yoke strip 1, and two limb strips 2 that are bevelled at one end but straight. at the other. Layers of the same shape are stacked upon each other in alternately 180 reversed positions to form the core structure.

Minor departures from the illustrated shapes are permissible without essentially impairing the advantageous effects. Particularly, a relatively smaller width of the yoke laminations may be sufficient.

If it is desired to give the core an enlarged iron cross section in the yoke portions, the spaces between the rectangular limb strips 8", i.e. the interstices between the yoke strips 7, may additionally be filled by likewise rectangular yoke strips '7" as shown in FIGS. 4 and 5. The iron cross section of the yokes is then larger than the iron cross section of the limbs.

For instance, an enlargement of the yoke cross section of only 50% is obtained with a design according to FIGS. 4 and 5. The frame-shaped core structure according to these figures has yoke strips 7 and 7" whose Width is only 1.5 times that of the limb strips 8, 8".

The invention may also be applied to multi-legged cores. A three-legged core designed in accordance with the invention is exemplified in FIG. 6.

Core structures according to the invention are mainly applicable for sheet material with a single preferred magnetic orientation, such as sheets of silicon iron, whose use necessitates composing the magnet core of individual strips so that the flux direction does not extend locally transverse to the flux direction. However, cores according to the invention are also advantageous for sheet material with two preferred magnetic orientations, for instance sheets of nickel iron, especially when the core size is so large that the individual layers of laminations, for reasons of manufacture, must be composed of individual strips.

Cores according to the invention are preferably used for transformers and reactors,-particularly in th end stage of a magnetic amplifier or in a direct-current premagnetized saturable'reactor such as used for controlling the operation of barrier-layer rectifiers. Especially desirable is the use of such cores in the switching or commutating reactors for pulse-controlled switches and contact rectifiers for which so far wound strip cores have almost exclusively been used.

I claim: 1

1. A jointed magnetizable core designed to avoid or minimize increase in magnetic induction at the joints,

comprising a frame forming a closed magnetic flux path,

the frame comprising limbs and yokes formed of a plurality of layers of assembled laminations formed lengthwise from strip material having a favorable magnetic direction lengthwise of the strip, the layers each comprising two limb strips and a yoke strip, the limb strips each having one diagonally disposed end edge and one substantially right-angled end edge, and the yoke strip having opposite diagonally disposed end edges, the diagonally disposed edges of the yoke strip adjoining, and being substantially coextensive with the diagonally disposed edges of the limb strips, the yoke strip being wider than the limb strips, the opposite diagonally disposed end edges of the yoke strip thereby providing, in conjunction wtih the diagonally disposed edges of the limb strips, two enlarged diagonally disposed joints, the adjacent layers of the frame being turned degrees to alternate, at the corners, the said wider yoke strips with theright angled end edges of the limb strips, the right-angled end edges of the limb strips in each layer extending substantially to an outer end edge of the core, the corner joints of each layer being overlapped by magnetic material of an adjacent layer, the limbs of the core having diagonally disposed joints only.

2. The magnetizable core defined in claim 1 in which the yoke strips are at least 1.5 times as wide as the limb strips, the opposing diagonally disposed edges of the yoke and limb strips being thereby further enlarged.

3. The magnetizable core defined in claim 1 in which the yoke strips are at least 1.5 times as wide as the limb strips, the opposing'diagonally disposed edges of the yoke and limb strips being thereby further enlarged, and there being no yoke lamination in alternate layers of the yoke.

4. A magnetizable core for electrical inductance devices, comprising a stack of lamination layers forming limbs and yokes in the shape of a rectangular frame, each of said layers being substantially U-shaped and being composed of one yoke strip and two limb strips, said yoke strip being trapezoidal to provide two non-parallel end edges, and each limb strip having at one end a bev elled edge adjoining an end edge of said yoke strip and having at the other end a rectangular edge, the end edges and the bevelled edges extending generally diagonally of the frame, alternate layers being stacked in mutually 180 degree reversed positions, with the limb strips so placed that the corner joints of each layer of the core are overlapped by magnetic material of an adjacent layer, and said yoke strips havinga width at least 1.5 times that of said limb strips. j

5. In a magnetizable core according to claim 4,.said laminations having a preferred magnetic orientation in the flux direction, said yoke laminations having about twice the width of said limb laminations and there being no yoke lamination in intermediate layers of the yoke.

References Cited in the fileof this patent UNiTED STATES PATENTS Switzerland Oct. 1, 1953 

